FIG. 23 shows a sectional view illustrating a structure of a conventional capacitor to be used for applications similar to the foregoing ones. Capacitor element 20 is formed by rolling the following members: a pair of electrodes in a polarized electrode layer formed on a current collecting unit made of aluminum foil are prepared with a separator disposed between the pair of electrodes, and each of the pair of electrodes protrudes in opposite directions. To be more specific in FIG. 23, an end of a first electrode of the pair of electrodes protruding in opposite directions contacts the inner bottom face of metal housing 21, and an end of a second electrode of the pair contacts a face of lid 22 made of aluminum.
FIG. 23, viewed from the front, shows an anode and a cathode brought out from the top and the bottom, namely, the respective end faces of capacitor element 20. Capacitor element 20 and driving electrolyte (not shown) are enclosed in metal housing 21 made of aluminum, of which the bottom face has cathode terminal 21a for outer connection. An end face near to the cathode of capacitor element 20 is electrically and mechanically coupled to the inner bottom face of metal housing 21 by laser welding.
The conventional capacitor includes lid 22 made of aluminum, and lid 22 has anode terminal 22a for outer connection. An end face near to the anode of capacitor element 20 is electrically and mechanically coupled to an inner face of lid 22 by laser welding. An insulating member is disposed between the rim of lid 22 and opening 23 of metal housing 21, and those three elements are curled together for sealing.
As discussed above, the conventional capacitor has anode terminal 22a and cathode terminal 21a along the center axis of metal housing 21 (along the vertical direction in viewing FIG. 23 from the front), and both the terminals are used for connecting to an outer device. Use of coupling member 24 called a bus-bar for coupling anode terminal 22a to cathode terminal 21a (shown in FIG. 24) allows plural capacitors to be connected together, thereby forming a capacitor unit to be used in a vehicle-mounted backup power supply.
Prior art related to the present invention is disclosed in, e.g. Unexamined Japanese Patent Publication No. 2000-315632.
Use of conventional capacitors in a capacitor unit formed of plural capacitors coupled together as shown in FIG. 24 makes anode electrode terminal 22a be coupled to cathode electrode terminal 21a, and at that time respective terminals are brought out in opposite directions to each other. As previously described, coupling member 24 called a bus-bar couples anode terminal 22a and cathode terminal 21a together. This requires a cumbersome work, and coupling spaces h1 and h2 must be prepared at both the ends, so that an unexpectedly large mounting space is needed. As a result, the capacitor unit cannot be downsized.
The anode terminal and the cathode terminal can be brought out in the same direction for overcoming the foregoing problems. For example, a polarized electrode layer is formed on the current collecting unit made of aluminum foil. In such a construction, a pair of electrodes are coupled to lead members to the outside respectively, and the pair of electrodes are rolled, so that the anode electrode and the cathode electrode can be brought out in the same direction. However, the electrode is brought out from one spot (or plural spots) of a belt-like elongated electrode, so that a resisting component becomes greater than that of a structure called an end face current-collection, i.e. electrodes are brought out from the entire end face of capacitor element 20. This method is thus not always good for a capacitor unit formed by coupling plural capacitors together.
FIG. 25 shows a sectional view illustrating another structure of a conventional capacitor. FIGS. 26A, 26B, 26C and 26D show a structure of a terminal plate to be used in this capacitor, i.e. they are a perspective view of the surface of the plate, a perspective view of the inner face thereof, a sectional view taken along line A-A, and a sectional view taken along line B-B in FIG. 26B, respectively. In FIG. 25 and FIGS. 26A-26D, hollow section 40a is disposed at about the center of capacitor element 40. Although this is not shown in the drawings, capacitor element 40 includes a pair of electrodes, i.e. anode and cathode formed in a polarized electrode-layer on a current collecting unit made of aluminum foil. The anode and the cathode are shifted in opposite directions from each other, and a separator is disposed between them, and those three elements are rolled together (not shown). The anode and the cathode are brought out through either one of the end-faces of capacitor element 40 respectively (from the top and the bottom of FIG. 25 viewed from the front).
Capacitor element 40 and driving electrolyte (not shown) are housed in closed-end cylindrical metal housing 41 made of aluminum. Protrusion 41a is formed integrally with the inner bottom face of housing 41 such that it fits into hollow section 40a of capacitor element 40. Protrusion 41a is fitted into hollow section 40a, and then the end face of capacitor element 40 on the cathode side is coupled electrically and mechanically to the inner bottom face of housing 41 by laser welding.
Anode electrode 42a to be used for outer connection is unitarily formed with terminal plate 42 on the surface of plate 42 made of aluminum. On the end face of capacitor 40 on the anode side, coupling sections 42b are formed, protrusion 42c fitted into hollow section 40a of capacitor element 40 and safety valve mounting hole 42d working also as an electrolyte inlet are also provided. The end face on the anode side of capacitor element 40 is coupled mechanically and electrically to coupling sections 42b by laser welding. On the rim of terminal plate 42, an opening of metal housing 41 is curled together with sealing rubber 43 for sealing the opening.
The foregoing conventional capacitor allows anode terminal 42a to be brought out for external connection and allows the cathode terminal to be brought out through metal housing 41. Connection of a plurality of those capacitors forms a capacitor unit to be used as a vehicle-mounted backup power supply.
FIG. 27 shows a sectional view illustrating still another structure of the conventional capacitor of this kind. This capacitor has belt-like cathode terminal 44a to be used for outer connection and unitarily formed with the bottom plate of metal housing 44. Anode terminal 45a to be used for outer connection is extended to an outer rim of terminal plate 45 disposed on the top. The rim of plate 45 and an opening of metal housing 44 are curled together with an insulating member (not shown) in between for sealing. This is generally called a double curling process. Other structures than the foregoing ones remain unchanged from the capacitor shown in FIG. 25.
However, it is difficult to downsize the conventional capacitors because of the structure of terminal plate 42 (or terminal plate 45). In other words, as FIG. 26D details, in conventional terminal plate 42, an opening end of metal housing 41 is curled with sealing rubber 43 lying between the opening end and an outer rim of terminal plate 42, so that the outer rim is exposed outside. The top side to be sealed is referred to as a reference plane, and plural coupling sections 42b to be coupled to an end face of capacitor element 40 on the anode side are caved in from the reference plane, and the caved-in coupling sections are radially provided. The height between the end face of capacitor element 40 on the anode side and the upper end of metal housing 41 having undergone the curling process is an amount that is not negligible with respect to the total height of the capacitor. To be more specific, the height is a sum of a distance from the reference plane to coupling section 42b (equal to the caved-in depth) and a height of the processed sections both of the sealing rubber and metal housing 41.
In recent years, capacitors have been required to be downsized and yet to have a greater capacity, so that a greater height of capacitor element 40 cannot be allowed amid the environment where the height of capacitors are limited. As a result, it is extremely difficult to increase the capacity of capacitors as well as decrease the resistance thereof.
The present invention addresses the foregoing problems, and aims to provide capacitors that can be downsized, yet increase the capacity as well as decrease the resistance. The invention also provides a method of manufacturing the same capacitors.